1. Field of the Invention
This invention relates to corrosion prevention in stress-bearing cable members, for example, cable strands of the main cable of a suspension bridge. This invention is more particularly directed to a method of encapsulation of such cable members, especially where rusting has been a problem, for example, near the crotches of suspension cable wire strands.
2. Brief Description of the Prior Art
Wherever steel wire cables are used, such as in the main cables of suspension bridges, and the cables are exposed to weather, rusting or other corrosion of the cables can occur. The cables are usually coated to help exclude moisture, but water persists in entering the cable just the same. Normally, water will flow to the lowest points of the cable. In the case of the cable strands of the main suspension cables of a bridge, water tends to flow to the vicinity of the cable strand shoes at the shore anchorages, and also tends to flow to the bottom of the main cable catenary. For that reason, the most severe rusting has been detected in those areas.
In addition, suspender ropes or cables extend vertically from the main cables to the suspension bridge deck, and these cables can also experience rusting at the lower ends thereof. Optional cables, such as anti-sway cables, can be included in some suspension bridges and these cables also require protection from rust at their lower portions.
In order to form a plug to prevent rusting of the wires at the lowest ends of the cable members, a paste encapsulation method has been previously proposed. In this previously-proposed method, an anti-rust medium, such as red lead paste, is applied under pressure to the desired sections of the cable members so that the red lead paste or other medium will enter voids in the cable member to form the desired plug.
In order to carry out such method, a steel split pipe, several feet in length is fabricated. Pressure ports are included in the pipe, and rubber gaskets are provided at the ends thereof. The split steel pipe is bolted or clamped in place over the cable member, and the red lead paste is applied at the ports at a nominal pressure of 4500 psi. In theory, pressure forces the red lead paste into the voids between the strand wires. After a sufficient time has passed, the steel pipe is removed and the excess red lead is scraped from the surface of the cable member.
Unfortunately, this previously-proposed encapsulation method has not provided sufficient protection. In fact, when wedges have been driven into a cable member so treated in order to inspect the strand wires within the cable member, it has been found that not all of the wires thereof were coated with the red lead paste. In those wires not coated, rusting had occurred.
Accordingly, an improved method of paste encapsulation has been sought which would be suitable for application to cable members, such as the wire strands of a suspension bridge main cable. However, no suitable such method has been discovered prior to this invention.